This invention relates to filled .alpha.-olefin/vinylidene monomer interpolymer compositions, and fabricated articles thereof.
Fillers are frequently used to improve the stiffness of polymer compositions, or to decrease the coefficient of linear thermal expansion, or to decrease the overall cost of the polymer composition. However, such fillers are well known to simultaneously decrease impact performance or toughness of the resultant composition. For example, Joseph A. Randosta & Nikhil C. Trivedi in Talc [published in Handbook of Fillers and Reinforcements for Plastics 160 (Harry S. Katz & John V. Milewski eds.)] confirm that the impact performance of polymeric materials is generally decreased by the presence of rigid fillers, especially below the glass transition temperature (Tg) of the matrix material, due to the fillers' action as "stress concentrators".
Typically, the filler is incorporated at levels ranging from 1 to 50 weight percent of the formulation, depending upon the filler density. Furthermore, even at relatively high levels of filler loading (e.g., greater than about 20 percent), typical thermoplastic formulations (e.g., polypropylene, an elastomeric rubber and talc) have very poor impact performance and do not function well in uses such as automotive facia. Low temperature impact resistance generally becomes more critical when the formulation is exposed to temperatures approaching the glass transition temperature of the rubber used in the formulation. Sometimes the room temperature impact resistance may even increase for highly filled formulations, but the low temperature impact resistance decreases rapidly with decreasing temperature.
The patent application WO 95/09945 discloses a thermoset elastomer composition which comprises a cross-linked substantially random interpolymer of (a) 15 to 70 weight percent of an .alpha.-olefin, (b) 30 to 70 weight percent of a vinylidene aromatic compound and (c) 0 to 15 weight percent of a diene. The linked substantially random interpolymer is typically mixed with a filler, an oil, and a curing agent at an elevated temperature to compound them. The amount of the curing agent is typically from about 0.5 to 12 weight percent, based on the total weight of the formulation. Carbon black may be added in an amount of up to 50 weight percent, based on the total weight of the formulation, to mask the color, to increase the toughness and/or to decrease the cost of the formulation. The disclosed thermoset formulations are useful in hoses, air ducts, brake cups, roofing materials and as various automotive parts, such as tires and moldings. However, the post-extrusion curing results in a cross-linked thermoset part that can not be reprocessed as a thermoplastic. This limits recyclability of the product.
U.S. Pat. No. 5,576,374 discloses filled thermoplastic olefinic compositions which have good low temperature impact performance and modulus. They comprise
(A) a thermoplastic resin selected from the group consisting of thermoplastic polyurethanes, polyvinyl chlorides, styrenics, engineering thermoplastics, and polyolefins,
(B) at least one substantially linear ethylene/.alpha.-olefin polymer which is characterized as having:
a) a melt flow ratio, I.sub.10 /I.sub.2, .gtoreq.5.63, PA1 b) a molecular weight distribution, M.sub.w /M.sub.n, defined by the equation: M.sub.w /M.sub.n .ltoreq.(I.sub.10 /I.sub.2)-4.63, and PA1 c) a critical shear rate at onset of surface melt fracture of at least 50 percent greater than the critical shear rate at the onset of surface melt fracture of a linear ethylene /.alpha.-olefin polymer having about the same I.sub.2 and M.sub.w /M.sub.n, and
(C) at least one filler.
The filled thermoplastic olefinic compositions are said to be useful as automotive bumpers, facia, wheel covers and grilles and freezer containers.
In view of the wide ranges of desirable properties and uses for thermoplastic polymers, it would be desirable to provide new filled polymer compositions.